This invention relates to a method and apparatus for making continuous metal filaments, particularly amorphous metal filaments, by depositing a molten stream of metal onto the inner surface of an annular chill roll while it is being rotated around its axis to form a solid filament on that surface, and withdrawing the filament.
For purposes of the present invention, a filament is a slender body whose transverse dimensions are much less than its length. In that context, filaments may be bodies such as ribbons, sheets or wires, of regular or irregular cross section.
It is already known to make metal filaments by directing a jet of molten metal against a moving chilled quenching surface whereon it is solidified. One of these known methods involves chill roll casting wherein a free jet of molten metal is impinged upon the exterior surface of a rotating drum, whereon it is solidified to form a filament, which is then flung away from the drum by centrifugal action. Chill roll casting techniques employing the exterior surface of a rotating drum or cylinder have, for example, been described by Strange and Pim in U.S. Pat. No. 905,758. Filaments formed on the exterior surface of a rotating drum may be recovered therefrom by using nipping means, as disclosed in U.S. Pat. No. 3,856,074 to Kavesh. The procedure described by Strange et al. may be readily employed to form filaments of many of the polycrystalline metals which possess sharp melting points, that is to say, which have solid-liquid transition range of less than about 5.degree. C. However, amorphous or glassy metals often have a transition range in the order of about 400.degree. C. or more, through which the viscosity of the metal gradually increases until the critical glass transition temperature is reached, and it is necessary for the filament to be quenched below its glass transition temperature before departure from the quench roll. This is often difficult to achieve by the procedure of Strange et al. because centrifugal force tends prematurely to fling the filament away from the drum surface.
Pond and Madden in Trans. Met. Soc. AIME, 245 (1969), pages 2475-6, describe a method for making metal filaments by directing a jet of molten metal against the inner surface of a rotating cylinder. The location of the jet is moved along the length of the cylinder, thereby producing a spiraling specimen of filament on the inner cylinder wall. Radial acceleration imparted to the liquid stream by rotation of the cylinder induces good thermal contact and spreads the stream into a flat filament prior to complete solidification. No provisions are made for stripping the filament from the drum as it is being produced, so that continuous production of filament is not possible, and the length of the filament so formed is inherently limited.
U.S. Pat. Nos. 3,881,542 and 3,939,900, both to Polk et al., are respectively directed to method and apparatus for making continuous length shaped metal filaments by casting a stream of molten metal within a groove formed in the inner periphery of a rotating cylindrical chill roll. U.S. Pat. No. 3,881,540 to Kavesh describes a process and apparatus for making continuous untwisted length of metal filament by casting a molten stream of metal onto the inner surface of an annular chill roll which inner surface is inclined at an angle of 2.degree. to 30.degree. to the axis of rotation of the chill roll, exerting pressure on the quenched molten stream in contact with the inclined inner surface of the chill roll after solidification, and collecting the filament thus formed.